This invention relates to a fastening apparatus and method in which load-induced elastic deformation of a supporting frame is at least partially compensated, in order substantially to maintain a desired relationship of cooperable fastening members supported on respective spaced arms of a frame.
Apparatus for forming joints in workpieces, such as sheet metal, by so-called deformational fastening such as riveting, self-piercing riveting, or clinching, is well-known and is widely used in the automotive industry, for example. A fastening device used in such apparatus may comprise punch and die members mounted on respective arms of a C-frame, for example.
The shape of components to be joined to one another may necessitate a variety of positions of a tool (e.g., die) mounted by a holder on one frame arm opposite to a punch on another frame arm. In addition, a change in the maximum width of an opening between the punch and the tool is often required for optimal adaptation of a fastening device for different tasks.
In apparatus disclosed in DE 10 2004 005 884 A1, tool holders of different lengths are interchangeably mounted on an arm of a frame in order to change the tool position within the frame opening. In addition, the holder of a punch drive can be attached to another arm of the frame in two different positions to provide different distances from an opposing tool. In this way, the width of an opening between the punch and an opposing tool can be further changed.
The support of tools by tool holders of different lengths, the different positions of a formed joint relative to the frame, and the different positions of the punch drive have the result that when loads are applied to the frame in a fastening or joint-forming operation, the longitudinal axis of the punch on one arm of the frame and the longitudinal axis of a tool on the other arm of the frame deviate from their original in-line relationship by different amounts. Such angular deviations can affect a joint being formed, because the opposing faces of the punch and the tool vary from their initial parallel relationship as a function of the angular deviations. Such deviations can significantly degrade the quality of a joint and should not exceed a specific amount. Moreover, it is desirable that angular deviations, of an acceptable order of magnitude, be kept as close to equal as possible, and not depend on the position of a joint being formed within the frame opening.
Loading of the frame during a fastening or joint-forming operation may also produce an offset of a joint relative to the frame, i.e., perpendicular to the longitudinal axes of a punch and a cooperable tool. Such offsets can produce undesirable loads on parts being joined and on equipment carrying the frame, for example a robot, and should therefore be kept as small as possible irrespective of the joint positions.